Extinct moa co-existed in pre-human New Zealand because they had a diverse range of diets and feeding strategies, New Zealand and Australian researchers have found.
New research, published today in Proceedings of the Royal Society B, London, combining CT and MRI scans and software used after the Canterbury earthquakes has detailed the likely diet and feeding strategy of five of the nine known species of moa.
The extinct megafauna ranged in size from the upland moa – about the size of a sheep – to the South Island giant moa which clocked in at up to 240 kilograms. But the study’s authors concluded that differences in the structure and strength of each species’ bill drove differences in diet and foraging, rather than overall size.
Canterbury Museum senior natural history curator Professor Paul Scofield said the most complete moa skulls from Canterbury Museum’s and Te Papa’s collections were scanned using medical CT (Computed Tomography) scanners.
That gave the researchers a base from which to produce highly accurate 3D models of the skulls. Because none of the skulls were perfectly intact to begin with, digital cloning was used to reconstruct the missing pieces.
But skulls, of course, are missing a key ingredient: muscles.
That’s where the University of Auckland’s Dr Peter Johnston came in. He made medical MRI (Magnetic Resonance Imaging) scans of mummified remains of moa from which the musculature was digitally reconstructed.
Finally, software used after the Canterbury earthquakes to identify weak or unsound buildings was employed to test the strength and structure of each species’ skull and infer biting and feeding behaviours. The results were surprisingly diverse, said University of New England’s Dr Marie Attard.
“The little bush moa had a relatively short, sharp-edged bill and was superior among moa at cutting twigs and branches, supporting the proposition that they primarily fed on fibrous material from trees and shrubs.”
“At the opposite extreme, the coastal moa had a relatively weak skull compared to all other species which may have forced them to travel further than other moas in search of suitable food, such as soft fruit and leaves,” Attard said.
Flinders University’s Dr Trevor Worthy said scientists had been limited in their efforts to determine anatomical function by examining bones, but new technology “allows us to bring new life to old bones and to get one step closer to understanding the birds they came from”.
Is there a replacement for moa?
What role the oversized herbivores played in pre-human New Zealand has continued to fascinate ecologists, with some thoughts that deer could have replaced their role and others speculating that birds like emu could be used as substitutes.
However, the researchers compared moa with cassowaries and emu and concluded that other ratites would be poor replacements for New Zealand’s missing megafauna. At best, they said, other species could only partially fill the void and would not restore ecosystem function.
Whanganui Regional Museum curator of natural history Dr Mike Dickison said the new findings would go some way to dispelling remarks about deer filling the same ecological niche as moa once did in New Zealand.
“We already knew that several species of moa lived side by side almost everywhere in New Zealand and that they had very different body sizes, diets, and bill shapes – some of this paper’s results are not news.”
“But this mechanical analysis of their bills suggests moa had a wider range of feeding strategies than we thought, and most must have fed in a very different way to living giant flightless birds such as the cassowary and emu,” Dickison said.
“This is important because emus have been suggested as a possible ecological surrogate that could replicate the effect of moa browsing in New Zealand forests. Emus have even been used experimentally to test if our plants are adapted to resist moa browsing, but those experimental results look more dubious now.”
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